Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $212.51   4.124%   $221.2739   $221.27   $221.25   $221.30  
  Purchase #2 $85.79   13.118%   $97.0439   $97.04   $97.05   $97.00  
  Purchase #3 $90.26   13.522%   $102.465   $102.47   $102.45   $102.50  
  Purchase #4 $192.77   3.367%   $199.2606   $199.26   $199.25   $199.30  
  Purchase #5 $214.51   4.623%   $224.4268   $224.43   $224.45   $224.40  
  Purchase #6 $73.55   12.824%   $82.9821   $82.98   $83.00   $83.00  
  Purchase #7 $80.70   3.179%   $83.2655   $83.27   $83.25   $83.30  
  7 purchase totals = $950.09       $1,010.7178   $1,010.72   $1,010.70   $1,010.80